A lithium metal phosphor oxide (LMP) is a material that is expected to be used as a cathode active material of a lithium secondary battery.
Examples of a method for preparing the LMP include a solid-state reaction and a sol-gel method.
The solid-state reaction is a method for preparing the LMP by mixing solid-state reaction raw materials and performing heat treatment, and has a problem in that since a heat treatment temperature is high and the reaction raw materials having fine particles having a size of several hundreds of nanometers should be used to prepare uniform nano-particles, dependence on the reaction raw materials is increased, and thus price competitiveness is degraded. Further, in the case of the solid-state reaction, since heat treatment itself should be performed in a reduction atmosphere, particular attention is required. Further, a conductive material needs to be applied on a surface of an LMP particle in order to implement a battery property because electric conductivity is low due to a material property of the LMP, and in the case where the solid-state reaction is used, there is a problem in that it is difficult to perform this surface coating.
The sol-gel method is a method for preparing the LMP by preparing metal alkoxide raw materials in a sol state, gelating the metal alkoxide raw materials through a condensation reaction, and then drying and heat treating the gelated metal alkoxide raw materials, and since costs of the used reaction raw materials are high and the sol-gel method is a reaction based on an organic solvent, a preparing cost is high.
Therefore, the present inventors have studied a novel synthesis method capable of solving the aforementioned problems, and found that in the case where the lithium metal phosphor oxide is synthesized by using a crystalline iron phosphate (FP) or a metal-doped crystalline iron phosphate (MFP), which is prepared by applying a high-gravity level of shearing force, as a precursor, a crystalline lithium metal phosphor oxide can be synthesized at a temperature that is even lower than a temperature when an amorphous iron phosphate hydrate is used as a precursor due to structural similarity of the precursor and a product, and growth of particles can be controlled at a low calcination temperature, and thus a process cost can be reduced, thereby accomplishing the present invention.